Preparation of fish meal from raw material and isolating fish oil from the same is well a known method and the technology currently used have been used for many decades. The process and device involves separation of the oil and removal of water from the raw material initially containing typically 75% water, 5% oil and 20% of dry matter. In general the raw material is brought to a boiling point in a cooker. The material obtained from the cooker is transferred to a press to squeeze out as much liquid as possible from the solid phase. The liquid phase is further separated in a decanter into a phase of solids and water on one hand and an oil phase on the other hand. The water is then removed from the solid/water phase in a drier and evaporators. The solid phase from the press is mixed with the solid phase from the evaporators and transferred into driers and then cooled down after drying.
U.S. Pat. No. 4,344,976 discloses a typical process for recovery of meal of high protein quality and oil from fish, where heating of the fish mass is carried out in any conventional way, and oil is separated from the heated fish mass by means of a centrifuge provided with a separate outlet for separated oil phase. In this publication the stick water and sludge discharged from the centrifuge are fed together to an evaporation unit where the mixture of sludge and stick water is fed through one or several indirectly heated tubes. The internal walls of which are continuously cleaned by means of a scraping device and the outlet of which is connected to a separation space for steam and evaporated product. The product is then further dried in conventional drying step.
Production of high quality low-heat generated fish meal requires that the process is performed at low temperature in the later stages of the process. In the early stages, where the water content is above 40%, the temperature of the material is at 100° C. as it passes through the boilers. When the oil phase and part of the water has been removed, the rest of the process is performed at low temperature to preserve the proteins.